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| United States Patent |
5,258,792
|
|
Suzuki
, et al.
|
*
November 2, 1993
|
Viewfinder for camera
Abstract
This invention provides a viewfinder which is mounted separately from a
taking lens on a camera and wherein the occupying space of a
parallax-correcting prism is minimized to arrange freely its optical
design. And also, this invention provides a viewfinder decreasing the
difference of the diopter and the fuzziness of the image between normal
photographing mode and macro photographing mode. To achieve these objects,
this viewfinder comprises a prism arranged in the optical path of said
viewfinder to correct the parallax, and a driving mechanism to slide said
prism in the direction normal to the axis of said lens system.
| Inventors:
|
Suzuki; Nobuharu (Aichi, JP);
Morisawa; Tahei (Tokyo, JP);
Abe; Tetsuya (Tokyo, JP)
|
| Assignee:
|
Asahi Kogaku Kogyo Kabushiki Kaisha (Tokyo, JP)
|
| [*] Notice: |
The portion of the term of this patent subsequent to November 3, 2009
has been disclaimed. |
| Appl. No.:
|
871695 |
| Filed:
|
April 21, 1992 |
Foreign Application Priority Data
| Jul 26, 1989[JP] | 1-193304 |
| Feb 22, 1990[JP] | 2-41460 |
| Current U.S. Class: |
396/377; 396/384; 396/386 |
| Intern'l Class: |
G03B 013/14 |
| Field of Search: |
354/219-225,199
|
References Cited
U.S. Patent Documents
| 3836934 | Sep., 1974 | Suzuki et al. | 354/222.
|
| 4129369 | Dec., 1978 | Kobayashi et al. | 354/221.
|
| 4164369 | Aug., 1979 | Urano et al. | 354/219.
|
| 4219264 | Aug., 1980 | Rodeck | 354/295.
|
| 4924247 | May., 1990 | Suzuki et al. | 354/221.
|
| 4944030 | Jul., 1990 | Haraguchi et al. | 354/222.
|
| 4967219 | Oct., 1990 | Morisawa et al. | 354/221.
|
| 5117247 | May., 1982 | Nakai et al. | 354/222.
|
| 5160954 | Nov., 1992 | Suzuki et al. | 354/221.
|
| Foreign Patent Documents |
| 2363796 | Jul., 1974 | DE.
| |
| 2740929 | Mar., 1979 | DE.
| |
| 60-33541 | Feb., 1985 | JP.
| |
| 60-70411 | Apr., 1985 | JP.
| |
| 710967 | Jun., 1954 | GB.
| |
| 87-07038 | Nov., 1987 | WO | 354/222.
|
Other References
"Parallax Correction" (Ruben), Research Disclosure, vol. 2244, No. 249, p.
57, Jan. 1985.
|
Primary Examiner: Gray; David M.
Attorney, Agent or Firm: Sandler Greenblum & Bernstein
Parent Case Text
This application is a continuation of application Ser. No. 07/557,062,
filed Jul. 25, 1990, U.S. Pat. No. 5,160,954.
Claims
What is claimed is:
1. A viewfinder adapted to be mounted on a camera separate from a
photographing lens of said camera, said viewfinder comprising:
a lens system having an optical axis;
a prism for correcting parallax between the photographing lens and said
lens system and being adapted to be selectively disposed along said lens
system optical axis;
said prism comprising a curved surface having a magnifying power for
corrected parallax and changing the diopter of said lens system when an
object is being photographed in close-up photography; and
driving means for inserting said prism into said optical axis of said lens
system upon close-up photography and for extracting said prism from said
optical system of said lens system upon normal photography.
2. The viewfinder according to claim 1, said lens system comprising a
variable power optical system.
3. The viewfinder according to claim 1, further comprising means, extending
transversely to said optical axis for guiding said prism for slidable
movement by said driving means.
4. The viewfinder according to claim 3, said guiding means comprising
spaced guide rails positioned along the path of movement of said prism.
5. The viewfinder according to claim 3, said guiding means comprising rails
extending transverse to said optical axis for guiding said prism.
6. The viewfinder according to claim 1, further comprising a close-up
photographing lever mounted for movement in a direction substantially
traverse to said lens system optical axis.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a viewfinder mounted on a camera separately from
a taking lens, and more specifically to a viewfinder having a prism for
correcting a parallax relative to the taking lens upon a macro
photographing mode.
2. Description of the Prior Art
Heretofore there has been a camera including a viewfinder separated from a
taking lens such as a lens shutter camera or a still video camera. The
viewfinders of these conventional cameras have in principle parallax by
the difference in the direction of optical axis from that of the taking
lens. This parallax can vary according to the distance from a camera to a
photographic object, and is needed to decrease in actual photographing.
Besides a normal photographing mode, some of the conventional cameras have
a macro photographing mode for taking a short-distance object which can
not be taken by the normal photographic mode.
Since a normal mode camera is preset to minimize the parallax for normal
photographing, it has high quantity of parallax in the short distance for
macro photographing.
In order to minimize this parallax upon macro photographing, some of the
conventional cameras have a rotatable correcting prism by standing across
the optical path of the viewfinder and other cameras have a movable visual
field frame in the viewfinder optical system.
FIG. 12 shows a schematic view for inserting a prism. This reversed
Galilean zoom viewfinder has a first lens group 41, a second lens group 42
movable for variable power, and an eyepiece group 43. The magnification of
the viewfinder is changeable according to that of a taking lens. The
parallax is decreased by inserting the prism 44 between the first lens
group 41 and the second lens group 42 and thereby bends its optical path
to the taking lens side upon macro photographing.
FIG. 13 is a schematic view showing the moving of the visual field frame of
a viewfinder. This zoom viewfinder has a first lens group 51, a second
lens group 52 movable for variable power, a Porro prism for erecting
images, and an eyepiece 54. A visual field frame 55 is mounted in the
vicinity of the image formation position of a photographic object. The
parallax upon macro photographing is corrected by moving the visual field
frame in the direction normal to the optical path and thereby an accurate
visual field is gained.
Referring to FIG. 12, the prism on the optical axis is rotated in order to
insert into the optical path and to extract from the path, and requires a
comparatively wide space for its rotation at the same time. Therefore the
lens-arrangement is restricted by this space.
In FIGS. 12 and 13, a high magnification of the viewfinder causes a great
difference between the diopter (i.e., the magnification power of the
viewfinder) upon macro photographing to a short distance object, and that
upon normal photographing to a standard distance object. A range of the
above difference often surpasses the adjustable range of the diopter of a
photographer's eye. Since a standard diopter is preset generally within
the available distance for normal photographing, a large change of the
diopter for macro photographing from a standard diopter makes fuzziness of
an image in the viewfinder upon macro photographing.
When the distance to a photographic object is defined as U, measured in
meters, the standard object distance for setting a diopter is defined as
U.sub.o measured in meters, and the magnification of the visual field in
the viewfinder is defined as M, the diopter difference between one object
located at U.sub.0 and another object located at U will be as follows:
.DELTA.D=(U.sup.-1 -U.sub.0.sup.-1)M.sup.2
For example, when M=1.2, U.sub.0 =3 m, and the standard diopter D=-1, are
each defined, the result is .DELTA.D=0.96, and D=-1.96 in the macro mode
in the case of U=1.
Both a high magnification of the viewfinder and a large difference between
the standard distance for adjustable diopter and the actual distance
requires much change from the standard diopter. Recently, zoom ratio, in
another word, a difference between the focal distances of a short focal
distance side and a long focal distance side, intends to become large.
Therefore, the diopter upon macro photographing by long focal distance to
a short distance object largely changes from standard diopter for normal
photographing.
SUMMARY OF THE INVENTION
To resolve the foregoing problems, the first object of the present
invention is to provide a viewfinder wherein the occupying space of a
parallax-correcting prism in the lens group is small and accordingly the
optical design can be freely carried out.
The second object of the invention is to provide a viewfinder which can
decrease the difference from the standard diopter and diminish the
fuzziness of the image.
To achieve the first object, a viewfinder for a camera of this invention is
characterized to be constituted so that a parallax correcting prism is
disposed to slide in the direction normal to the axis of the finder lens
group for inserting into the optical path and extracting from it.
To achieve the second object, a viewfinder of this invention is further
characterized in that at least one surface of the prism is powerful and
curved. In this constitution, the image of the viewfinder upon macro
photographing can be cleared by setting the curvature of the prism surface
so as to diminish the difference between the diopters of
macro-photographing and normal photographing.
Although the prism can be inserted in a optional position, the fuzziness of
the image through the finder lens group can be diminished by inserting the
prism into the object side rather than into the viewfinder lens group
because of changelessness of the axis of the viewfinder lens (i.e., the
optical axis is thus not changed internally of the viewfinder when the
prism is inserted in front of the object lens of the viewfinder).
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective side view showing the whole constitution of a
camera including a viewfinder according to the present invention;
FIG. 2 is a plan view showing an arrangement of the optical elements of a
viewfinder;
FIG. 3 is a side view of FIG. 2;
FIG. 4 is a schematic view of FIG. 2;
FIG. 5 is a plan view of a prism for a viewfinder in the embodiment;
FIG. 6 is a front view of a prism for a viewfinder in the embodiment;
FIG. 7 is a perspective side view of a viewfinder in the embodiment as
viewed from an object side;
FIG. 8 is a perspective side view of a viewfinder in the embodiment as
viewed from an eyepiece side;
FIG. 9 is a plan view showing a slide plate part in the embodiment;
FIG. 10 is a plan view showing a click plate part in the embodiment;
FIG. 11 is a plan view showing a prism driving mechanism in the embodiment;
FIG. 12 is a schematic view showing an arrangement of optical elements of a
viewfinder using the conventional prism;
FIG. 13 is a semitic view showing an arrangement of optical elements of a
viewfinder not using the conventional prism;
DETAILED DESCRIPTION OF THE EMBODIMENT
The embodiment of the present invention will be described hereinafter with
reference to the accompanying drawings.
FIGS. 1 through 11 show the embodiment adapting the present invention to a
zoom viewfinder.
FIG. 1 shows a camera including a viewfinder in accordance with the present
invention, and the numerals 1, 2, and 3 designate a camera body, a taking
lens, and a viewfinder respectively. In the embodiment, the side mounting
the taking lens 2 is defined as a front side 1a, and the side mounting the
viewfinder through which a photographer gazes is defined as a back side
1b. The broad surface of the upper part of the body is defined as an upper
surface, mounting a release button and a zoom lever. The broad surface of
the lower part of the body 1 is defined as a lower surface 1c, mounting a
macro lever 4 for switching a camera mode between modes of macro and
normal photographing. The macro lever 4 is disposed on the position where
the photographer can operate it with the thumb F in having the camera.
The taking lens 2, of which focal distance can be changed by operating a
zoom lever, is a zoom lens. The lens 2 can be disposed or a suitable
position for macro photographing upon a macro photographing mode.
Referring to FIGS. 2 and 3, the optical system of the viewfinder 3 has the
arrangement of the order from the object side of a first lens group 10
having a negative power, a second lens group 11 having a positive power as
a whole of the adhered lenses, a third lens group 12 having a positive
power, a mirror 13, a Porro prism 14 for erecting an image, and an
eyepiece lens 15. The first and second lens groups 10 and 11 are disposed
to move in the direction of the optical axis Ax in order to change the
magnification of the viewfinder 3. And the visual field of the viewfinder
can be changed by the lens groups' moving in the direction of the axis
according to the zooming of the taking lens 2.
FIG. 4 shows a schematic plan view of the viewfinder optics including the
Porro prism 14. The 1st through 3rd lenses comprise an object optical
system. A visual field glass 15, on which frames for the visual field and
for measuring the distance, etc., are each drawn, is disposed in the
vicinity of an image-formation surface by the object optical system.
A prism 20 is slidably disposed in the front of the first lens group 10 in
order to insert into or deflect from the optical axis of the viewfinder 3.
As shown in FIGS. 5 and 6, the prism 20 is formed in the shape of the
letter L when seen in a plane view of the prism or in the shape of a
rectangle when seen in the front view of the prism. Portions of the prism
inserted in the axis are a curved surface having a predetermined power in
the object side surface 21, a plane predetermined power in the object side
surface 21, a plane slanting at a predetermined angle to the lens system
axis Ax in the surface 22 of the first lens group 10 side, and an
approximately wedged shape in a sectional surface of the sliding direction
of the prism 20. The wedge shaped section of the prism 20 can best be
visualized by viewing a cross-section as revealed by a section line
extending horizontally through the FIG. 6 view of the prism. The curved
surface 21 is a convex spherical surface having a large radius of
curvature which is predetermined so that the difference between the object
diopters upon macro and normal photographing decreases. The surface of the
curved surface 21 can be formed in not only a spherical surface but also a
non-spherical surface in order to correct an aberration or the like.
A pair of guide pins 23, 24 projecting upward and downward are each mounted
on the upper and lower surfaces of the prism 20, and a cam-follower pin 25
is also mounted on the lower surface of the edge portion. The prism 20 is
slidingly inserted in the front of the lens system and then bends the
optical axis of the viewfinder to the axis of the taking lens side for
correcting the parallax and controlling the difference from the standard
negative diopter by changing to a plus diopter upon macro photographing.
The insertion of the prism 20 in the front of the lens system does not have
a bad effect on the function of the lens system because of changelessness
of the optical axis in the lens system. Therefore the inferiority of the
viewfinder image can be checked. On the other hand, the insertion in the
middle of the lens system makes the inferiority of the viewfinder image
because of the change of the axis between the insertion and extraction.
The description on the mechanical constitution of a viewfinder will be
given in accordance with FIGS. 7 through 11.
FIG. 7 is a perspective view of the viewfinder as viewed from a
photographic object.
The viewfinder 3 has a casing 5 including the foregoing lens system in the
inside and comprising a frame unit 6 having a slidable first lens group
10, and a frame unit 7 having a slidable second lens group 9. Each frame
units 6 and 7 is constituted slidably in the sliding axes 6a and 7a fixed
to the casing. Each frame units is driven by a driving mechanism (not
shown ) connected with the stopping pins 6b, 7b according to zooming of
the taking lens.
On the surface facing to the object of the casing 5, a pair of guide rails
are mounted along the line from the optical axis of the viewfinder to the
front side 1a of the camera body 1. These guide rails have guide grooves
8a, 9a engaging guide pins 23, 24 of the prism 20. And the rails are
disposed both upper side and lower side of the optical path of the
viewfinder. A pair of the rails 8, 9 cross the optical path of the
viewfinder. A straight part of these rails crosses the optical path, and a
curved part of the rails is disposed out of this path. The prism 20 can
move slidably by the guide rails 8, 9 and thereby insert into or extract
from the optical path of the viewfinder.
The boxes A, B fixed to the casing on the upper and lower positions on both
sides of the prism are a light-emitting unit and a light-receiving unit
respectively to measure the distance to the photographic object, as shown
in FIG. 7.
Hereinafter, the mechanism for driving the prism 20 will be described.
Referring to FIG. 8, a macro lever 4 projecting from the lower surface 1c
of the body is fixed to a slide plate 30 mounted inside the body. The
prism 20 can slide by operating the macro lever 4 via a delivering
mechanism 31.
A slide plate 30 fastening the macro lever 4 is formed approximately
rectangular-shaped and can go back and forth in the direction D1
(direction vertical to the viewfinder axis) in which the photographer's
thumb F bends. As shown in FIG. 9, the slide plate 30 is constituted of a
engaging protuberance 30a for giving a click-like impression in sliding by
a click plate 32, and a engaging pin 30b for engaging with the delivering
mechanism. In FIG. 10, a elastic click plate 32 formed in the T-shape is
constituted of a lug hole 32a for the camera body, and engaging holes 32b,
32c for engaging with the protuberance 30a of the slide plate 30. The part
of the click plate 32 facing to the slide plate 30 can be movable in the
upward or downward direction D2 in FIG. 8. The engaging holes 32b, 32c
have a function of determining a first and second stop positions.
In FIGS. 8, 11, the delivering mechanism 31 for delivering the motion of
the slide plate 30 to the prism comprises an attaching shaft 32d fixed to
the body 1 and a driving lever 33 movably attached to the attaching shaft
32d. The driving lever 33 comprises two fork-shaped arms 33a, 33b
extending each other in the opposite direction. One arm 33a is engaged
with the engaging pin 30b of the slide plate 30 by the slot portion formed
in its tip. And another 33b, bending its tip into a U-shape in order to
compensate the difference of the height between the prism 20 and the slide
plate 30, is engaged with a projecting cam follower pin 25 of the prism 20
penetrating the guide rail 9 through a long and narrow hole 33d in the
tip.
The function of a prism-sliding mechanism of the viewfinder according to
the embodiment will be hereinafter described on FIGS. 8 and 11.
The slide plate 30 is disposed on the position as shown by a dotted line in
FIG. 11 by operating the macro lever upon normal photographing. The
engaging protuberance 30a of the slide plate 30 is engaged with the
engaging hole 32b of the click plate 32, and the slide plate is disposed
on the first stop position, and then the prism 20 is disposed on the
position outside the optical path of the viewfinder upon normal
photographing.
On the other hand, the slide plate 30 is moved by the macro lever to the
position of a phantom line (two-dot-and-chain line) in FIG. 11 upon macro
photographing. This moving makes the driving lever 33 pivot from the solid
line position to the phantom line position in FIG. 11, and consequently
the prism 20 is slide into the optical axis of the viewfinder along the
guide rail. When the prism 20 is disposed completely inside the optical
axis, the engaging protuberance 30a of the slide plate is engaged with the
engaging hole 32c of the click plate 32 and the slide plate 30 itself is
disposed on the second stop position.
In this embodiment, a photographing can be quickly operated by the
switching from the normal mode to the macro mode with the thumb F, because
the macro lever 4 is mounted on the lower surface 1c of the camera body 1.
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